Disable ArticleFeedback (v4)

I'm still a little worried that there are hidden dependency relationships
between AFTv5 and AFTv4, so I'm not removing the configuration variables just
yet, but am simply marking the extension as inactive everywhere. If this goes
well, we can remove the configuration variables entirely in a subsequent
change.

Bug: 43892
Change-Id: I82fe6063a24ee4cba13778b7b88a29e3c0f1296e